1. Field of the Invention
This invention relates to a method for forming undercoating to repair a damaged portion on a vehicle.
2. Description of the Prior Art
A conventional undercoating method for repairing a damaged vehicle by painting includes many processes for undercoating and is complicated, consequently to demand considerable technique and skill in a worker. Besides, the conventional method inevitably turns out to prolong the time required for working and raise the costs of using tools and materials.
To be concrete, the existing repairing method comprises the following processes. That is, the method comprises removing an old coating layer formed around a damaged portion such as a scratch or scrape in an automobile body, processing tapering the verge portion from which the old coating layer is removed into a smooth slanting (feathering edge) surface (hereinafter referred to as xe2x80x9csmoothing processxe2x80x9d), applying polyester putty (poly-patty) to the damaged portion, which is formed into the feathering edge, to further smooth the damaged portion, sanding the damaged portion coated with poly-patty, further applying primer surfacer (pra-saf) to the damaged portion sanded, polishing the damaged portion coated with the primer surfacer, further applying lacquer patty thereto, and then polishing it (generally called a filler process). First, the problems encountered on the filler process will be enumerated hereinafter, and thereafter, the problems encountered on the smoothing process will be enumerated.
1. Filler Process
(1) Number of Processes
The method requires three different types of fillers although these fillers have a common role for smoothing the damaged portion. Namely, six works of applying the fillers and sanding in all, and therefore, often become onerous where these processes are performed.
(2) Problem on Polyester Patty
The work of applying the polyester patty must be performed with a spatula or knife since the polyester patty is high viscous, and necessitates a high technique for uniformly applying it to a panel having a complicated surface. Besides, the polyester patty has a drying mechanism of a two-pack polymerizing type. That is, it is formed of a main agent and a curing agent, which are stored in different containers. These patty materials are respectively taken out from the containers onto a working platen in use, and uniformly mingled by using the spatula. However, in mingling the patty compositions, air comes into the patty to form air bubbles in the patty. As a result, this process entails a problem such that air pores are formed in a hardened patty, which are exposed to a repaired surface by finally grinding the surface.
(3) Primer Surfacer
The primer surfacer is applied for plugging sandpaper scratches resulting from sanding the hardened polyester patty, preventing sinking of topcoating, preventing corrosion, and making sure of adhesive properties of coating composition. However, the primer surfacer is lower in viscosity than the polyester patty noted above and includes much solvent and diluent, possibly resulting in imbibition on the old coating layer and a defect in the coating layer. To avoid this disadvantage, it is necessary to apply a sealer to the coating surface and sanding the surface coated with the sealer. Consequently, the work is disadvantageously complicated. Furthermore, since the primer surfacer has low viscosity and includes much solvent and diluent, it easily permeates into the pores in the porous polyester patty, resulting in bringing about the so-called sinking phenomenon. As a result, large and deep pores and/or sandpaper scratches left in the surface of the hardened polyester patty could not be plugged completely.
(4) Lacquer Patty
The lacquer patty is applied for plugging small scrapes or pores left after grinding with primer surfacer. However, the lacquer patty has low viscosity and quick-drying property, and therefore, must be applied quickly and thinly by using the spatula. The work of applying the lacquer patty quickly and thinly requires a high technique and much skill. Besides, the lacquer patty has a solvent evaporation type drying mechanism and is weak in resin bonding power. Therefore, topcoating lacquer is sunk under the surface, consequently to form a lusterless topcoating surface. It is necessary to apply primer surfacer to the surface and polish the final repairing surface in order to solve such a disadvantageous phenomenon, consequently to increase the number of processes required.
(5) Area Repaired
Since this method requires many processes as noted above, the area, which is repaired by repeating the processes of applying various fillers and polishing the repairing surface, is resultantly increased. Thus, this method is disadvantageous in that the repaired area finally becomes remarkably larger than the initial area of the damaged portion to be repaired primarily.
Polishing Process
The polishing process for finishing the repairing surface principally requires a work of wet rubbing (manual polishing). This work which should be carried out by small amounts possesses the drawback of decreasing its efficiency. Besides, the wet rubbing work possibly brings about a blister (bulging) on the coating surface. Furthermore, the polishing process disadvantageously causes harm to an environment since it discharges a large volume of polluted water including the coating composition.
(7) Working Tool
Since this method requires a large number of processes, many kinds of tools such as a sanding machine and some sandpapers are used. As a result, this method entails problem such that the work becomes complicated, thus to increase production costs.
In Japanese Patent Publication No. SHO 56-23664 relating to an improvement in a filler process as noted above, there is disclosed a repairing and coating method for repairing a coating defect portion or the like of an automobile body by uniformly spraying a spray patty composed of unsaturated polyester resin and a curing agent onto the surface to be repaired, polishing the surface after dried, applying a topcoating composition onto the surface, and then drying the surface with the topcoating. The prior art invention provides a simplified filler process in which coating and polishing is easily carried out by the use of spray putty in place of the polyester putty, primer surfacer and lacquer patty, which should be processed repeatedly. However, the prior art invention proposes a mere improvement in the putty composition, and makes use of the conventional sanding and polishing processes. Thus, it could not sufficiently develop the efficiency of the work of performing the filler process, and therefore, has not been put into practice because the finished surface of the coating resultantly becomes rather rough.
2. Sheet Metal Process
In the sheet metal process, the damaged coating (old coating) is removed and the verge portion from which the old coating is removed is subjected to a feathering edge treatment. Recently, this work requires antithetical processes of scraping and smoothing the surface to be repaired by using two types of sanding machines such as a single-action sanding machine and a double sanding machine, which are provided with different sandpaper disks.
Thus, the conventional sheet metal processing work is composed of a plurality of processes, resulting in decreasing the working efficiency, regardless of the fact that the processes have the essentially common functions of sanding and polishing by use of the sanding machines and sandpaper disks.
In the light of the foregoing circumstances, the present invention has an object to develop a method of working such as coating and polishing, patty compositions, and tools, and provide a method for forming undercoating in repair coating in order to simplify repairing processes, shorten working time, decrease costs of tools and materials for use therein, and form a finish surface of high quality.
Specifically, the present invention has another object to provide putty compositions capable of formation of a thick coating layer, which could not be achieved so far.
The present invention has further object to provide an undercoat forming method for preventing an area to be repaired from becoming larger than the initial area of the damaged portion to reduce an area finally repaired to a minimum.
To attain the objects described above, according to the present invention, there is provided a method for forming undercoating in repair coating on a damaged portion of a vehicle, comprising removing an old coating from the damaged portion, subjecting a verge portion of the damaged portion from which the old coating is removed to a feathering edge treatment, spraying putty composition composed of 100 parts by weight of main agent, which contains 25 to 40 percent by weight of unsaturated polyester resin and 23 to 13 percent by weight of reactive diluent so as to have a viscosity of 0.1 to 3.0 Pa.s, and 1 to 4 parts by weight of curing agent, to form a coating layer of about 1 mm at most, drying the putty sprayed, and dry-sanding the putty dried. This method is featured in that the processes of spraying the putty and dry-sanding the dried putty are performed respectively in only one operation.
That is, the putty consisting of the compositions noted above used in this invention has excellent spraying property, so that it can be sprayed thick and uniformly. Besides, the process of dry-sanding the dried putty enhances the efficiency of polishing. Consequently, the entire processes including the processes of spraying the putty and dry-sanding the dried putty, which are carried out in one operation, respectively, can be simplified and shortened in working time. Furthermore, the finally repaired area can be kept to a minimum in comparison with the initial area of the damaged portion.
The average grain size of the abrasive ground for use in the dry-sanding process is preferably 30 to 60 xcexcm.
According to the method mentioned above, the putty can be polished efficiently, and the polished surface can be maintained flat.
Furthermore, in the dry-sanding process, a straight sanding machine provided with an abrasive base of polyester film can be used. The use of the polyester film enables the smoothness of the repaired surface to be improved.
Also, in the method of the invention, epoxy adhesives can be used as a fundamental adhesive agent, and urethane adhesives can be used as an upper coating adhesive.
The aforementioned method results in effects such that vibration easily propagates from the base of the abrasive ground to the abrasive grain, and abrasive chips are shaken off owing to the elasticity of upper coating adhesive.
Furthermore, the process of removing the old coating on the damaged portion and the process for subjecting the verge of the damaged portion from which the old coating is removed to the feathering edge treatment can be carried out by use of a double-action sanding machine. It is preferable to use the double-action sanding machine with the abrasive ground having the average grain diameter of 110 to 120 xcexcm.
According to the method mentioned above, the process of removing the old coating and the feathering-edge process can be efficiently performed by use of one sanding machine. The smoothness of the ground and polished surface can be maintained.
Other objects and features of the present invention will be hereinafter explained in detail with reference to the accompanying drawings.